The use of sulfonated naphthol- or sulfonated phenol-formaldehyde condensation products as acid-dye-resist, levelling, or wet-fastness agents for polyamide textile substrates is well known in the art. Because of their acid-dye-resist properties, these condensation products, when applied to polyamide textile substrates, act as stain-resist agents against subsequent staining by foodstuffs containing acid-dye colorants. (Materials and compositions which act to render such substrates resistant to acid dyes are referred to alternatively herein as stain-resist agents or stain-resist compositions.)
One particular class of stain-resist compositions which comprise mixtures of sulfonated phenol-formaldehyde condensation products with a hydrolyzed copolymer of maleic anhydride and one or more ethylenically unsaturated aromatic monomers is described by Fitzgerald, Rao, Vinod and Alender U.S. patent application, Ser. No. 07/280,406, now U.S. Pat. No. 4,883,889. The entire disclosure of this application, which is subject to an obligation of assignment to a common assignee, is hereby incorporated by reference herein.
Compositions containing stain-resist agents may be applied to polyamide substrates using a variety of methods, including application to filaments in a spin-finish during fiber manufacture, application to a yarn or a textile substrate such as tufted carpet in a dye bath as, for example, in a beck apparatus, or application following dyeing in a beck or continuous dyeing process. Processes for applying the stain-resist compositions described in the aforementioned U.S. patent application are taught by the same inventors in their divisional application, Ser. No. 07/280,404, now refiled as Ser. No. 07/465,40. Polyamide substrates made stain-resistant by such compositions are the subject of another divisional application, Serial No. 07/280,405, now refiled as Serial No. 07/426,933. The entire disclosure of each of these applications, which are also subject to an obligation of assignment to a common assignee, is hereby incorporated by reference herein as well.
When stain-resist compositions are applied in batch processes, such as in a beck, they may be used at relatively high dilution factors since the amount of time the substrate is immersed in the bath is typically on the order of thirty minutes to an hour which is sufficient to achieve good exhaust and good fixation of the stain-resist agent onto the substrate. Because of the high liquor to goods ratio in the bath, a wide range of pH values (typically 2-5) may be used to achieve acceptable stain-resistance in the finished product. However, the long residence times required to achieve adequate exhaust and fixation of the stain-resist agent onto the substrate limit the degree of productivity that can be achieved in a batch process This, combined with increased water consumption and effluent-treatment problems make it desirable to apply stain-resist agents in a continuous process.
Stain-resist compositions may be applied to polyamide (or polyamide-containing) textile substrates such as carpets in continuous processes using any of a number of widely-known apparatus designed for liquid application to a moving web via immersion, spraying, or other means. Examples of such equipment include a Kusters Fluidyer.RTM., such as the type described in U.S. Pat. No. 4,576,112, which uses a flexible air bladder to push the carpet against a fluid application slot to achieve uniform and deep penetration of the fluid into the pile fabric. Another increasingly-common type of continuous applicator is a Kusters Flexnip.RTM. apparatus which is now widely accepted in the carpet industry as an effective means for application of stain-resist chemicals to dyed carpets. This class of applicator, which squeezes the carpet to apply the composition to the moving substrate, is described in the November 1987 issue of Carpet & Rug Industry.
To apply stain-resist agents in a continuous process, any apparatus or applicator may be used that provides adequate wet-out and uniform application of the fluid throughout the tufted carpet structure. The stain-resist solutions may be applied using such an apparatus in a second pass through the continuous dye line in which the stain-resist solution is substituted for the dye solution in the dye applicator, or in a single pass by including in the line a separate applicator for applying the stain-resist after dyeing. The stain-resist solution may also be added to the dye solution itself to effect the application in a single pass. Alternatively, stain-blocking agents also may be applied to beck-dyed carpets by installing an application apparatus, such as a Kusters Flexnip.RTM. prior to the wet goods drier.
When applying stain-resist agents in continuous processes such as those described above or others known in the art, stain-resist solutions of higher concentration than those effective in batch processes are typically required to achieve acceptable stain resistance since such processes use lower temperatures, significantly shorter residence times, and lower liquor to goods ratios. When stain-resist solutions comprising mixtures of sulfonated phenol-formaldehyde condensation products and hydrolyzed copolymers of maleic anhydride and one or more ethylenically unsaturated aromatic monomers are applied to textile substrates in a continuous process, it is desirable that the pH of the stain-resist solution be less than about 3. If the pH is greater than about 3, insufficient exhaust and/or poor fixation of the stain-resist agents is obtained so that the finished substrate exhibits an unacceptably low degree of acid-stain resistance, either initially, after washing or both. However, when the pH of these stain-resist compositions is reduced to below about 3, the hydrolyzed maleic anhydride copolymers precipitate out of solution at the concentrations required to achieve acceptable stain resistance in continuous application processes. This significantly reduces the amount of active ingredient available to treat the carpet or substrate resulting in poor stain resistance in the finished substrate.